Polyalkylene carbonate resin is polymer material useful for packaging material or coating material and the like. A method of preparing polyalkylene carbonate resin from an epoxy compound and carbon dioxide is eco-friendly in that noxious compound phosgene is not used and that carbon dioxide can be obtained in the air.
Thus, many researchers have been developed various forms of catalysts in order to prepare polyalkylene carbonate resin from an epoxy compound and carbon dioxide.
A document (Polymer Journal, 1981, vol 13, p 407) describes a method for preparing synthetic resin using carbon dioxide as raw material, wherein reaction products of zinc hydroxide and various organic carboxylic acid are used as catalyst.
However, when polymerization is progressed using the catalyst described in the document, there were problems in that polymerization activity is low, polymerization medium is not homogeneous, and thus, PDI is high, and a long polymerization time is required.
Although polyalkylene carbonate is generally prepared by bulk polymerization using an organic metal catalyst, the polymerization may be conducted in a batch type, semi-continuous type, or continuous-type, and the polymerization may be conducted in two or more stages with different reaction conditions.
Even if these various methods are applied, the concentration of polymer in the solution increases as the reaction progresses, the produced high molecular weight polymer increase the viscosity of the solution, and thus, a catalyst cannot be uniformly dispersed in the reactant. Thus, excessive epoxide monomers compared to a catalyst should be used, and recovered and separately treated.
In addition, after bulk polymerization, when a solvent is additionally introduced so as to reduce the viscosity of produced polymer, high molecular weight polymer is converted into a uniform polymer solution, and thus, it takes long time to reach a viscosity at which the polymer can be transferred from a polymerization reactor and removed, and when the polymer with high viscosity is agitated, the motor of an agitator may be overloaded at the initial stage thus affecting a continuous process.
In addition, since an epoxy compound used in the reaction has high reactivity, it is difficult to control reaction heat by the existing bulk polymerization, and thus, it is difficult to apply for a scale up process while controlling the reaction.
It is known that the polymerization initiation temperature of ethylene oxide is about 100° C., reaction heat of 2324 kJ/kg is generated during autopolymerization, and heat capacity of ethylene oxide is 0.749 cal/g-K.
Particularly, pure ethylene oxide is known to be very highly reactive, and thus, when the one component is used in a large quantity, process danger may be caused. Thus, when the reactant is locally heated or contacts with cations or anions, due to the reaction heat generated by autopolymerization, explosive heating may be initiated. In addition, when large quantities of epoxide monomers react at elevated temperature, due to autopolymerization, they may be converted into polyalkyleneglycol thus degrading the physical properties of the final product.
Propylene oxide is also known to have reaction heat of 1500 kJ/kg during autopolymerization, and heat capacity of 0.495 cal/g-K (25° C., liquid), and thus, if pure propylene oxide is introduced in an excessive amount, it is highly probable that the large quantities of propylene oxide may be autopolymerized on the surface of a reactor, and thus, PPG and the like may be produced to adversely influence on the physical properties of resin.